The present invention relates to an in-axle rotational speed sensor assembly for mounting to a fixed or stationary ferromagnetic member such as a drive axle differential bearing adjustor having a central opening therethrough for receipt of a rotatable member such as a shaft for measurement of the rotational speed thereof. Wheel speed sensors have become increasingly important for providing an electric signal indicative of wheel speed for use with anti-lock brake systems (ABS), traction control, and differential lock-up systems in brake control systems, and the like. Typically, the sensor provides a wheel speed signal to a micro-processor-based control unit (ECU) as is well known in the art. Examples of such systems and/or sensors may be seen by reference to U.S. Pat. Nos. Re. 30,522; 3,961,215; 3,929,382; 3,556,610; 3,604,760; 4,585,280; 4,361,060; 3,768,840; 4,818,035; and 4,863,221, disclosures of which are incorporated herein by reference.
Typically, such rotational speed sensor assemblies are electromagnetic in nature, and rely on alignment of rotor teeth or spaces between rotor teeth rotating past the sensor to complete or break, respectively, the magnetic flux path to produce a digital or analogue signal indicative of the rotational speed of the motor.
Placement of wheel speed sensor assemblies within the axle (i.e., "in-axle") to protect same is also known, as may be seen by reference to U.S. Pat. Nos. 3,769,533; 4,724,935; 4,836,616; 4,862,025; and 4,862,028; disclosures of which are incorporated herein by reference.
Annular rotational speed sensor assemblies having an annular toothed stator/sensor surrounding a rotating toothed rotor, or vice-versa, are well known in the art. Annular speed sensor assemblies are preferred over single or multiple point type sensor assemblies in certain situations, as they provide a relatively high signal-to-noise ratio, tend to be self-compensating for run-out errors between the rotor and stator, and require little or no adjustment. Examples of such in-axle annular speed sensor assemblies may be seen by reference to U.S. Pat. Nos. 4,870,911; 4,027,753; and 4,689,557, the disclosures of which are incorporated herein by reference.
The annular speed sensor described in the above-referenced parent applications have provided for a low-cost sensor especially for use with drive axles at an inboard location where the sensor could easily be protected. However, some problems have been encountered in assembly in which certain parts of the sensor were deformed during mounting, and affected the signal output of the sensor; and, thus it has been desired to provide such an in-axle wheel sensor which can be easily and reliably assembled into the drive axle without requiring special tools or measurements during the assembly, and which is not distorted during assembly so as to affect the signal output.